1. Field of the Invention
The present invention is directed to a novel process for the direct cationic polymerization of biological oils, such as vegetable oils, to higher molecular weight products. Particularly, this invention relates to the cationic polymerization of biological oils, such as castor oil, corn oil, safflower oil, soybean oil, tung oil, and fish oil, and to copolymerization of these oils with other biological oils and/or other olefins. Polymerized biological oils can be used for preparation of polyols and other chemical species by introducing hydroxyl and other functional groups to ultimately produce elastomers, rubbers, and plastics from renewable resources.
2. Description of Related Art
The natural environment is being overwhelmed by non-biodegradable, petroleum-based polymeric materials. In recent years, there has been an interest in cheap, biodegradable polymeric materials made from readily available, inexpensive natural sources, such as fats and biological oils. See generally Larock, U.S. Pat. No. 6,211,315; U.S. Published Patent Application No. 2002/095007. The development of polymeric materials from biological oils, such as vegetable and fish oils, could dramatically expand and diversify the market for biological oils, while also improving the environment and reducing dependence on petroleum products.
Biological oils are triglycerides comprised of fatty acids. For example, soybean oil is comprised of three main unsaturated fatty acids: oleic acid, linoleic acid (also called linolic acid), and linolenic acid. The approximate composition of some common biological oils is set forth the following table. It will be appreciated that the composition may vary somewhat, depending on the source of the biological oil.
TABLE 1Fatty Acid Content of Common Biological OilsMid-OleicCanolaSunflowerSoybeanLinseedSunflowerCornFatty Acid ProfileoiloiloiloiloiloilLauric C12:00.02Myristic C14:00.040.090.050.030.06Myristoleic C14:1Palmitic C16:04.094.1110.885.485.5910.81Palmitoleic C16:10.210.050.070.060.060.11Heptadecanoic C17:00.050.040.090.050.050.09Heptadecanoic C17:10.090.040.040.040.010.03Stearic C18:01.863.794.183.524.461.85Oleic C18:156.1157.1522.6918.8822.1827.25Linoleic C18:221.0131.4052.4116.1064.2256.96Arachidic C20:00.600.250.260.120.240.30Eicosenoic C20:11.700.210.300.140.190.20Linolenic C18:37.890.316.0653.730.420.65Heneicosanoic C21:00.010.010.020.02Eicosadienoic C20:20.060.02Behenic C22:00.170.460.140.040.410.03Erucic C22:10.12Total C18:160.8558.6424.9520.1423.1528.19Total C16:1, C20:1, C22:1,2.080.260.370.200.250.31C24:1Total C18:221.3331.7952.7216.2164.8057.52Total C20:2, C22:20.060.000.020.000.000.00Total C18:38.460.336.2353.920.440.69Total C20:30.050.000.000.000.000.00Total Saturated Fatty Acids6.788.6915.609.2710.8513.10
Currently, the polymerization of some unsaturated biological oils (linseed oil, soybean oil, sunflower oil, canola oil, etc.) is largely carried out on industrial scale by two routes: thermal polymerization process (heat bodied oils) and air blown oil process.
Thermal polymerization of biological oils is carried out by simple heating the oils, under nitrogen, at very high temperatures (usually about 290-330° C.) for several hours, in the absence of any catalyst or initiator. Due to the high temperature, thermal polymerization of the double bonds in the unsaturated fatty acids of the oils takes place. The resulting products are called bodied oils. They have much higher viscosity than the initial oil and lower iodine value (a lower double bond content) as compared with the initial oil. Typically, the iodine value is about 65 for bodied soybean oil, and about 100 for bodied linseed oil. This process is applied industrially, especially for linseed oil. Unfortunately, the process has a high energy consumption due to the high temperatures needed. In addition, the thermal polymerization process takes a relatively long time, and the thermal degradation of the oil results in the formation of volatile low molecular weight compounds which are eliminated continuously by steam stripping under vacuum. The yield in final thermally polymerized oil is about 80-85% against the quantity of initial oils.
Air blown oils are obtained by bubbling air through the liquid biological oils (linseed oil, soybean oil, sunflower oil, castor oil, etc.) in the presence or in the absence of radical initiators, at about 100-110° C., for a relatively long time (30-50 hours). The viscosity of oil increases substantially, probably due to radical polymerization involving oxidative coupling through the allylic hydrogens and the double bonds of the unsaturated fatty acids in the oils. As a result, the iodine value of the air blown oil is much lower than the initial iodine value of the oil (e.g., about 80 for air blown soybean oil). In addition, an oxidative-degradative process of the oil takes place, resulting in the formation of various functional groups containing oxygen, such as aldehydes, ketones, hydroxyl, carboxyl, hydroperoxide, etc. The average molecular weight of the air blown oil is also relatively low, with the maximum being about 1300-1400 g/mol.
It also is known to cationically polymerize fatty acids (or their esters, mainly methyl esters) to obtain dimeric acids and trimeric acids in the presence of cationic catalysts. The majority of industrial processes used to synthesize dimeric and trimeric acids employ acidic activated clays (activated bentonites from the group of montmorillonite which is an acidic aluminium silicate, or magnesium silicate, 3-5% against oil) as catalysts in the presence of water at high temperatures (230-240° C.) over several hours (4 to 7 hours). The catalyst is filtered and reused, and the unreacted fatty acids are distilled, leaving behind about 50-60% dimer (C36) and trimer fatty acids (C54). Concerning the cationic polymerization of fatty acids with acidic clays, there is a large number of patents, such as Goebel, U.S. Pat. No. 2,482,761; Goebel, U.S. Pat. No. 2,664,429; Barrett et al., U.S. Pat. No. 2,793,219; Barrett et al., U.S. Pat. No. 2,793,220; Myers et al., U.S. Pat. No. 2,955,121; Fischer, U.S. Pat. No. 3,157,681; Conroy, U.S. Pat. No. 3,632,822; Milks et al., U.S. Pat. No. 3,422,124; Wheeler, U.S. Pat. No. 3,444,220; Turner et al., U.S. Pat. No. 4,937,320; Bermann, GB1353783; Hayes, GB2172597; and DiFranco, WO 00/50528.
For the polymerization of fatty acids and of methyl esters of fatty acids, there are some processes that use Lewis acids as catalysts, mainly boron trifluoride (BF3) or boron trifluoride diethyl etherate (BF3*Et2O). More specifically, Turner et al., U.S. Pat. No. 4,973,743 describes a process in which methyl soyate was polymerized at 20-25° C. in the presence of BF3 over three hours. The resulting polymeric product contained 25-33% monomer, 18-22% dimer, and 49-53% trimer and higher polymers. The polymerization of fatty acids and fatty acids esters with strong Lewis acids is also described in the scientific literature. See Croston et al., Polymerization of Drying Oils: Catalytic Polymerization of Fatty Acids and Esters with Boron Trifluoride and Hydrogen Fluoride, Journal American Oil Chemists Society, 331-333 (1952). Those researchers used 2% BF3 as a catalyst at 150-200° C. Ghodssi et al., Cationic Polymerization of Oleic Acid and its Derivatives. Study of Dimers, Bulletin de la Societe Chimique de France, 4 1461-1466 (1970) describes the cationic polymerization of methyl oleate at 20-30° C. with the formation of dimers and higher oligomers.
The cationic polymerization of biological oils by using boron trifluoride (BF3) as the catalyst is described in two patents. In Uloth et al., U.S. Pat. No. 2,365,919, soybean oil was polymerized at 130° C. in the presence of 2.8% BF3 as catalyst. A viscous product was obtained, with viscosity about five times higher than the initial viscosity of soybean oil. Under similar conditions, cottonseed oil was polymerized over six hours at 130° C. in the presence of 4% BF3 as catalyst. A polymerized product was obtained with a viscosity of about 10 times higher than the initial viscosity of oil. In Eichwald, U.S. Pat. No. 2,160,572, soybean oil was polymerized at 70° C. with 2% boron trifluoride over 50 hours. Another group lead by Professor Richard Larock has investigated the cationic copolymerization of natural oils (soybean oil, fish oil, tung oil, etc.) with some vinyl monomers, including styrene, divinyl benzene, norbornene, dicyclopentadiene, in the presence of BF3.Et2O (4-5%). Polymerization results in solid copolymers as generally set forth in Larock et al., U.S. Pat. No. 6,211,315 and Larock et al., U.S. Published Patent Application 2002/095007.
The present invention is directed to an improved process for the cationic polymerization of biological oils. In contrast to the use of the Lewis acid boron trifluoride (BF3) as the catalyst, the present invention employs a superacid as the catalyst, with tetrafluoroboric acid (HBF4), triflic acid (CF3SO3H), and hexafluoroantimonic acid (HSbF6) being especially preferred. The present invention provides superior and unexpected results, including short reaction times, much higher viscosity of the products, and milder reaction conditions. The biological oils are polymerized to higher molecular weight products consisting of monomers, dimers, trimers, tetramers, higher oligomers and polymers.